1. Field of the Invention
This invention relates in general to heating and dispensing materials, and in particular to devices for electromagnetically heating and dispensing materials.
2. Description of the Prior Art
Prior art devices have been utilized for heating and dispensing materials, such as for heating a solid material until it melts and then dispensing the material as a liquid. For example, hot glue guns are used for heating an end of a solid glue stick to a transition temperature at which the glue is liquefied and then dispensing the melted glue through a dispensing orifice. Typically, a housing is provided having an interior flow path through which the material is pushed as it is heated. Resistance heating elements are commonly used. The resistance heating elements have been mounted to the housing outside of the flow path, and often outside of the housing.
Other devices have utilized induction heating to heat materials for dispensing. A housing is usually provided having an interior flow path through which the material is pushed as it is heated. An electromagnetically heated susceptor is located either directly in or immediately adjacent to the material flow path. Induction coils have been mounted outside of the housings for inducing eddy currents to flow within the susceptors to generate heat for transferring to the materials. Often an external shroud is provided around the induction coil to protect an operator. Heat from passing current through the induction coil usually has to be removed to prevent overheating of the coil. Forced cooling is often used, resulting in wasted energy. External shrouds and cooling devices for induction coils also add additional weight and size to such prior art devices.
Inductive heating devices having large material flow capacities require that a large surface of the material be heated at one time. For melting materials, this results in susceptors having large heat transfer surface areas for contacting materials at melt faces for the materials. In order to prevent cold spots over the large heat transfer surface areas of such susceptors, the susceptors are made to have high heat capacities and high thermal conductivities. Although susceptors having high heat capacities in combination with high thermal conductivities add additional weight to prior art devices, they provide substantially uniform temperatures across the heat transfer surface areas, even those portions of the surface areas which are more remote from induction coils than others. However, when inductive heating of the susceptor is stopped, the large heat capacity of such susceptors will result in continued heat transfer to the material, often to a significant depth within the material beyond the melt face. This not only wastes energy, but may also result in waste of the material being heated.